b 1. Field of the Invention
This invention relates to a Fischer-Tropsch process for selectivity producing low molecular weight alpha-olefins utilizing an unsupported single phase Fe-Mn spinel catalyst promoted with Group IA or IIA metal salt in which the atomic ratio of Fe:Mn is 2:1 or above.
2. Brief Description of the Prior Art
Fischer-Tropsch processes have long been known to produce gaseous and liquid hydrocarbons containing C.sub.2 -C.sub.4 olefins. Because of the importance of C.sub.2 -C.sub.4 olefins, particularly as feedstocks for the chemical industry, modifications of the Fischer-Tropsch process are constantly being pursued toward the goals of maximizing C.sub.2 -C.sub.4 olefin selectivity with the particular objective of maintaining high catalyst activity and stability under the reaction conditions. The main thrust of the efforts in this area has been in the area of catalyst formulation.
Coprecipitated and/or supported iron-based catalysts, including those containing manganese, are known for producing C.sub.2 -C.sub.4 olefins. Examples of disclosures in the art directed to such iron-manganese catalysts and/or alloys include: W. L. vanDijk, et al., Appl. Catal., 2, 273 (1982); Eur. Pat. Appl. 49888 to Ruhrchemie (1981); H. J. Lehman, 73rd AIChe Meeting Paper #103D; W. D. Deckwer, et al., Chem. Ing. Tech., 53 (10) 818 (1981); V. Rao and R. Gormley, Hydrocarbon Processing, 139, November (1981); H. Kolbel and K. Tillmetz, U.S. Pat. No. 4,177,203 (1970); EPO Patent Publication No. 0,071,770; U.S. Pat. No. 2,605,275; U.S. Pat. No. 2,850,515; Prepr. Div. Pet. Chem. Am. Chem. Soc. (1978) 23(2) pp 513-20; Intersoc. Energy Convers. Eng. Conf. 1978, 13(1) pp 482-6; U.S. Pat. No. 4,186,112; EP 49,888; React Kinet. Catal. Lett. 1982, 20(1-2) pp 175-80; U.S. Pat. No. 2,778,845; Khim. (1) Tekhnol. Topliv i Masel (Russ.) 10(6) 5-10 (1965); UK Patent Appln. No. 2,050,859 A; German Patent Appln. No. OT 2919-921; Prace Ustavu Vyzkum Paliv 8, p. 39-81 (1964 ) (Czech).
An iron-manganese spinel of the formula, Fe.sub.2 MnO.sub.4, is reported as a catalyst component formed during Fischer-Tropsch synthesis in which a coprecipitated Fe/Mn oxide catalyst is initially employed in Applied Catalysis 5 (1983) pp. 151-170. However, this and the above cited references do not describe a Fischer-Tropsch hydrocarbon process initially employing an unsupported single phase Fe/Mn spinel catalyst having an Fe:Mn atomic ratio of 2:1 or above and being promoted with a Group IA or IIA metal salt promoter agent.
What is particularly desired in fixed bed Fischer-Tropsch processes are catalysts for selectively producing high levels of C.sub.2 -C.sub.4 olefins and low levels of methane under the desirable combined conditions of high catalyst activity and stability.